Carbon fibers are produced by heating (carbonizing) precursor fibers produced from, for example, polyacrylonitrile fibers, rayon fibers, cellulose fibers, or pitch fibers. Using precursor fibers produced from polyacrylonitrile fibers for example, carbon fibers are produced through an oxidization process for heating the precursor fibers in an oxygen atmosphere (inside an oxidization oven), and a carbonization process for heating the fibers resulting from the oxidization process (hereafter, oxidized fibers) in an inert atmosphere (inside a carbonization furnace). The fibers are heated while passing (being fed) through the oxidization oven and the carbonization furnace.
The carbonization process involves heating with, for example, an electric heater. While the atmosphere inside the carbonization furnace is being heated with an electric heater, oxidized fibers pass through the furnace and are heated indirectly.
The conditions for the carbonization process, including temperature and fiber stretching, are optimized to produce carbon fibers with various properties, such as tensile properties and compressive properties (e.g., Patent Literatures 1 and 2).